The following patent applications, which are assigned to the assignee of the present invention and filed concurrently herewith, cover subject matter related to the subject matter of the present invention and are incorporated herein by reference:
09/791,373 Barrel Assembly
09/791,651 Cradle For A Quick Barrel Change.
09/791,376 Force Isolating Cradle Assembly.
1. Field of the Invention
The present invention broadly relates to injection molding machines and, in particular to the injection unit of an injection molding machine. Injection molding machines include machines for injecting plastic material, or metal material, or metal material in a thixotropic state.
2. Summary of the Prior Art
Operation of an injection molding machine introduces a number of forces, pressures, and stresses on the injection unit. For example, axial carriage force is a force applied to engage the nozzle end of a barrel assembly against a sprue bushing of a mold. This provides a force sealing connection between the nozzle and sprue bushing preventing leakage of melted material during injection. Carriage force is applied and maintained prior to injecting the melt of material.
Injection force is a force directed along the length of a reciprocating screw located in a bore of a barrel assembly. Injection force results in injecting a melt of material into a mold. There is an axial reactive injection force acting along the length of the barrel assembly as a result of moving a screw forward during the injection stage of a molding process.
Injection pressure is a pressure required to overcome the resistance to the flow of the melt of material in the nozzle, runner system, and mold cavity. Injection pressure is exerted on the melt in front of the screw tip during the injection stage of a molding process. The accumulator end of a barrel assembly must withstand injection pressure.
Injection units for molding machines are very well known. For example, the book entitled xe2x80x9cInjection Molding machines A User""s Guide 3rd Editionxe2x80x9d by Johannaber was published in 1994 by Carl Hanser Verlag (ISBN 1-56990-169-4) and contains a detailed description of conventional injection units for plastic injection molding machines in Chapter 3 on pages 38, 39 42, 43, 44, 75, and 76. The reciprocating screw (RS) injection unit includes a barrel assembly which includes a nozzle, barrel head, barrel, axial bore, feed port, heater bands, and thermocouples. A reciprocating screw, which includes a non-return valve, is disposed in the axial bore of the barrel. The axial bore of the barrel includes a metering section and a feeding section. An electric or hydraulic drive operates the screw to feed and meter a melt of material and inject the metered material into a mold. The barrel assembly is fixed and supported, cantilevered, at one end of the barrel by a carriage. Hydraulic or electric actuators connect between the carriage and a frame member or fixed platen of the injection molding system. Operation of the actuators move the barrel assembly towards and away from the stationary platen and provides an axial carriage force through the entire length of the barrel during injection minimizing leakage between the nozzle tip and the sprue bushing. The axial reactive injection force is directed through the entire length of the barrel during injection.
The book entitled xe2x80x9cInjection Molding Operationsxe2x80x9d produced by Husky Injection Molding Systems Ltd., and printed in Canada, copyright 1980 also contains a description of conventional injection units for plastic injection molding machines on pages 41 through 44. Again, for the reciprocating screw injection unit, a barrel is supported at a distant end by a carriage, which houses the injection cylinder and a rotational drive. A hydraulic cylinder is connected between the carriage and a stationary platen. In operation of the hydraulic cylinder, the carriage force is applied along the entire length of the barrel. For a two stage injection unit, a barrel is supported at one end by a carriage. The carriage houses the drive. The nozzle of the barrel feeds into a shooting pot which includes an injection piston. The carriage supports another end of the shooting pot. A hydraulic cylinder is connected between the carriage and a stationary platen. In operation of the hydraulic cylinder, the carriage force is applied along the entire length of the shooting pot. The axial reactive injection force is directed through the entire length of the shooting pot during injection.
U.S. Pat. No. 5,040,589 issued on Aug. 20, 1991 to Bradley et al (assigned to The Dow Chemical Company). The patent describes an injection apparatus for injection molding a thixotropic semi-solid metal alloy. The patent contains a description of an apparatus for processing a metal feedstock into a thixotropic state as the metal is fed into a hopper, located at one end of the barrel, and transported into an accumulation zone located at another end of the barrel. The barrel is constructed of a single piece of material with thick walls. A number of heating zones are defined along the length of the barrel, including sections of the barrel having differing thickness. The feed throat area and zone 4 are relatively thick sections. Zone 3 is a slightly thinner section, and zone 2 is the thinnest section. The barrel is conventionally mounted in the injection unit. A feed throat end of the barrel is mounted in an upright support secured to the frame of an injection unit. A bottom surface of the barrel, intermediate the distant ends of the barrel, rests on a second support also secured to the frame. The carriage force is applied along the entire length of the barrel in operation of the apparatus. All sections of the disclosed barrel must be thick enough to withstand the combination of axial carriage force and axial reactive injection force directed through the entire length of the barrel during injection.
U.S. Pat. No. 5,983,978 issued on Nov. 16, 1999 to Vining et al (assigned to Thixomat Inc.). The patent describes a thixotropic metal injection molding apparatus. The barrel is formed in two sections to define a high pressure section and a low pressure section. The low pressure section is thinner than the high pressure section. A feed throat end of the barrel is mounted in an upright support of an injection unit. A bottom surface of the barrel, intermediate the distant ends of the barrel, rests on a second support also secured to the frame. The carriage force is applied along the entire length of the barrel in operation of the apparatus. All sections of the disclosed barrel must be thick enough to withstand the combination of axial carriage force and reactive injection force through the entire length of the barrel during injection.
There are a number of problems and deficiencies with the known prior art devices. Barrels are costly due to the amount of material required to provide a suitable thickness for withstanding the axial force along the entire length of the barrel. The axial force may be the carriage force, or the reactive injection force, or a combination of these two forces.
Special materials are required for barrels in use with thixotropic materials and these special materials are very expensive and are difficult to manufacture.
Thick barrels have a high thermal resistance which affects the efficiency and controllability of heating a material in the axial bore of a barrel.
Barrels, conventionally mounted in the injection unit, are typically difficult to install and remove. The process of installation and removal within a carriage is time consuming. Installation of the barrel in a carriage is further prone to alignment problems.
The primary objective of the present invention is to provide an improved barrel assembly for use in an injection molding machine.
Another primary objective of the present invention is to provide an improved carriage assembly for use in an injection molding machine.
Another primary objective of the present invention is to provide an improved injection unit for use in an injection molding machine.
Another primary objective of the present invention is to isolate a portion of a barrel assembly from axial forces.
Another object of the present invention is to reduce the cost of a barrel assembly.
Another object of the present invention is to reduce the amount of material required in certain sections of a barrel assembly.
Another object of the present invention is to reduce the weight of a barrel assembly.
Another object of the present invention is to reduce the axial stress in a portion of the barrel assembly.
Another object of the present invention is to reduce the thermal mass in a portion of the barrel assembly.
Another object of the present invention is to couple and support the barrel intermediate the ends of the barrel for providing more accurate alignment of a nozzle to the sprue bushing.
Another object of the present invention is to provide a carriage assembly permitting unobstructed access for installing and removing the barrel assembly.
Another object of the present invention is to provide a carriage assembly with a first coupler for securing the barrel assembly intermediate the ends of the barrel assembly to the cradle assembly.
Another object of the present invention is to provide a carriage assembly with a second coupler for retaining a portion of the barrel assembly to the cradle assembly.
Another object of the present invention is to provide a carriage assembly with a barrel support for aligning the barrel within the carriage assembly during installation of the barrel assembly with the carriage assembly.
An injection unit comprising an injection assembly mounted on an injection unit frame. The injection assembly includes a barrel assembly, a carriage assembly, and a drive assembly. The barrel assembly includes first and second barrel portions having an axial bore therethrough, and a first barrel coupler. The location of the first barrel coupler defines a boundary between the first barrel portion and the second barrel portion. The carriage assembly includes a first carriage coupler to engage the first barrel coupler, and a carriage actuator for linking with a stationary platen of a clamp unit. The drive assembly operated a screw disposed in the axial bore of the barrel assembly. In use, the first barrel coupler interlocks with the first carriage coupler to secure the barrel assembly in the carriage assembly, thereby isolating the second barrel portion from axial carriage force.
As an alternative, the injection unit may comprise a second barrel coupler, and a second carriage coupler. The second barrel coupler disposed on said second portion of the barrel. The second carriage coupler aligned with the lengthwise axial opening and the first carriage coupler, wherein the second barrel coupler and the second carriage coupler retain the barrel to the carriage intermediate an end of the barrel and the first barrel coupler.
As an alternative, the injection unit may comprise an axial force linkage member. The axial force linkage member disposed intermediate the first barrel coupler and the first carriage coupler wherein the axial force linkage member distributes axial force.
As an alternative, the injection unit may comprise a thermal isolator. The thermal isolator is disposed between the first barrel coupler and the first carriage coupler and reduces conductive heat transfer between the barrel assembly and the carriage.
As an alternative, the injection unit may comprise a linkage insulator. The linkage insulator disposed intermediate the first barrel coupler and the first carriage coupler wherein the linkage insulator distributes axial force and reduces conductive heat transfer between the barrel and the carriage.
As an alternative, the injection unit may comprise a barrel alignment member. The barrel alignment member aligned with the lengthwise axial opening wherein the barrel alignment member aligns the barrel with the carriage.
In another aspect of the invention, an injection molding machine consists of a clamp unit an injection unit, a barrel, a screw, a first barrel coupler, and a carriage. The carriage comprises a cradle member, a mounting surface and a first carriage coupler. The clamp unit for receiving a mold. The clamp unit operable between an open position, a closed position, and a clamped position. The injection unit for creating a shot of material for injection into the mold. The barrel having a first portion, a discharge end, an opening, and a lengthwise axial bore extending between the discharge end. The screw disposed in the lengthwise axial bore of the barrel. The screw rotatable and reciprocatable in the lengthwise axial bore of the barrel. The first barrel coupler disposed on the first portion of the barrel. The cradle member having a lengthwise axial opening for receiving the barrel. The mounting surface for mounting said carriage to the injection unit. The first carriage coupler aligned with the lengthwise axial opening wherein the first carriage coupler and the first barrel coupler secure the barrel to the carriage.
As an alternative, the injection molding machine may comprise a second barrel coupler, and a second carriage coupler. The second barrel coupler disposed on said second portion of the barrel. The second carriage coupler aligned with the lengthwise axial opening and the first carriage coupler, wherein the second barrel coupler and the second carriage coupler retain the barrel to the carriage intermediate an end of the barrel and the first barrel coupler.
As an alternative, the injection molding machine may comprise an axial force linkage member. The axial force linkage member disposed intermediate the first barrel coupler and the first carriage coupler wherein the axial force linkage member distributes axial force.
As an alternative, the injection molding machine may comprise a thermal isolator. The thermal isolator is disposed between the first barrel coupler and the first carriage coupler and reduces conductive heat transfer between the barrel assembly and the carriage.
As an alternative, the injection molding machine may comprise a linkage insulator. The linkage insulator disposed intermediate the first barrel coupler and the first carriage coupler wherein the linkage insulator distributes axial force and reduces conductive heat transfer between the barrel and the carriage.
As an alternative, the injection molding machine may comprise a barrel alignment member. The barrel alignment member aligned with the lengthwise axial opening wherein the barrel alignment member aligns the barrel with the carriage.
As an alternative, the first barrel coupler may include a linkage member. The first barrel coupler may also include a second linkage member. The linkage member may include a thermal isolator. In an embodiment of the invention, the linkage member is a pair of standoffs. In another embodiment of the invention, the linkage member is a ring.
In an embodiment of the invention, the second barrel coupler is a recess formed in an outer surface of the second portion of the barrel. In another embodiment of the invention, the recess is a substantially flat pad. In another embodiment of the invention, the recess forms a spline. In another embodiment of the invention, the recess is an axially aligned slot.
As an alternative, the first carriage coupler comprises a yoke coupler and a cradle coupler. The yoke coupler is disposed on the yoke and the cradle coupler is disposed on the cradle member. The yoke coupler and the cradle coupler engage the barrel for securing the barrel to the carriage.
As an alternative, the yoke coupler is an engaging surface formed on a side of the yoke opposite the cradle coupler. In an embodiment of the invention, the engaging surface is a barrel seat formed in a central opening of the yoke.
As an alternative, the cradle coupler comprises a fit upright support and a second upright support. The first upright support and the second upright support are separated by an opening for receiving the barrel. The first upright support and the second upright support secure the barrel to the carriage.
As an alternative, the first upright support includes a first coupling surface and the second upright support includes a second coupling surface wherein the first coupling surface and the second coupling surface engage a coupling surface of the barrel.
As an alternative, the second carriage coupler includes an engagement member for retaining the barrel.
As an alternative, the engagement member includes a first coupling member and a second coupling member. The first coupling member and the second coupling member are separated by an opening for receiving the barrel. The first coupling member and the second coupling member retain the barrel to the carriage.
As an alternative, the first coupling member includes a first coupling surface and the second coupling member includes a second coupling surface.
In an embodiment of the invention, the first coupling surface and the second coupling surface are a flat recess for engaging a complimentary surface of the barrel.
As an alternative, the second carriage coupler includes a retaining plate releasably secured to the cradle member for retaining the barrel in the carriage.
As an alternative, the barrel alignment member aligns the barrel axially and aligns the barrel vertically in the cradle.
As an alternative, the barrel alignment member includes a first barrel support member and a second barrel support member. The first barrel support member and the second barrel support member support the barrel at a predetermined height in the carriage.
As an alternative, the first barrel support member includes at least one standoff and the second barrel support member includes at least one standoff.
Further objects and advantages of the present invention will appear hereinbelow.